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From: Bjorn Helgaas <helgaas@kernel.org>
To: "Pali Rohár" <pali@kernel.org>
Cc: "Thomas Petazzoni" <thomas.petazzoni@bootlin.com>,
	"Lorenzo Pieralisi" <lorenzo.pieralisi@arm.com>,
	"Andrew Murray" <amurray@thegoodpenguin.co.uk>,
	"Bjorn Helgaas" <bhelgaas@google.com>,
	"Marek Behún" <marek.behun@nic.cz>,
	"Remi Pommarel" <repk@triplefau.lt>,
	"Tomasz Maciej Nowak" <tmn505@gmail.com>,
	Xogium <contact@xogium.me>,
	linux-pci@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] PCI: aardvark: Don't touch PCIe registers if no card connected
Date: Wed, 1 Jul 2020 16:34:42 -0500
Message-ID: <20200701213442.GA3662456@bjorn-Precision-5520> (raw)
In-Reply-To: <20200701082044.4494-1-pali@kernel.org>

On Wed, Jul 01, 2020 at 10:20:44AM +0200, Pali Rohár wrote:
> When there is no PCIe card connected and advk_pcie_rd_conf() or
> advk_pcie_wr_conf() is called for PCI bus which doesn't belong to emulated
> root bridge, the aardvark driver throws the following error message:
> 
>   advk-pcie d0070000.pcie: config read/write timed out
> 
> Obviously accessing PCIe registers of disconnected card is not possible.
> 
> Extend check in advk_pcie_valid_device() function for validating
> availability of PCIe bus. If PCIe link is down, then the device is marked
> as Not Found and the driver does not try to access these registers.
> 
> This is just an optimization to prevent accessing PCIe registers when card
> is disconnected. Trying to access PCIe registers of disconnected card does
> not cause any crash, kernel just needs to wait for a timeout. So if card
> disappear immediately after checking for PCIe link (before accessing PCIe
> registers), it does not cause any problems.

Thanks, this is good.  I'd really like a short comment in the code as
well, because this sort of link-up check tends to get copied to new
drivers where it shouldn't be used, e.g., something like this:

  /*
   * If the link goes down after we check for link-up, nothing bad
   * happens but the config access times out.
   */

> Signed-off-by: Pali Rohár <pali@kernel.org>
> 
> ---
> Changes in V2:
> * Update commit message, mention that this is optimization
> ---
>  drivers/pci/controller/pci-aardvark.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c
> index 90ff291c24f0..53a4cfd7d377 100644
> --- a/drivers/pci/controller/pci-aardvark.c
> +++ b/drivers/pci/controller/pci-aardvark.c
> @@ -644,6 +644,9 @@ static bool advk_pcie_valid_device(struct advk_pcie *pcie, struct pci_bus *bus,
>  	if ((bus->number == pcie->root_bus_nr) && PCI_SLOT(devfn) != 0)
>  		return false;
>  
> +	if (bus->number != pcie->root_bus_nr && !advk_pcie_link_up(pcie))
> +		return false;
> +
>  	return true;
>  }
>  
> -- 
> 2.20.1
> 

  reply index

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-28 14:31 [PATCH] " Pali Rohár
2020-05-28 16:26 ` Bjorn Helgaas
2020-05-28 16:38   ` Pali Rohár
2020-05-28 16:49     ` Bjorn Helgaas
2020-05-29  8:30       ` Pali Rohár
2020-06-30 12:31         ` Pali Rohár
2020-06-30 13:51     ` Bjorn Helgaas
2020-06-30 14:04       ` Pali Rohár
2020-06-30 14:58         ` Bjorn Helgaas
2020-07-01  8:08           ` Pali Rohár
2020-07-01  8:20 ` [PATCH v2] " Pali Rohár
2020-07-01 21:34   ` Bjorn Helgaas [this message]
2020-07-02  8:23     ` Pali Rohár
2020-07-02  8:30 ` [PATCH v3] " Pali Rohár
2020-07-09 11:35   ` Lorenzo Pieralisi
2020-07-09 12:22     ` Pali Rohár
2020-07-09 14:47       ` Lorenzo Pieralisi
2020-07-09 15:09         ` Pali Rohár
2020-07-10  9:18           ` Lorenzo Pieralisi
2020-07-10 15:44             ` Pali Rohár
2020-07-10 16:08               ` Bjorn Helgaas
2020-07-10 19:30                 ` Pali Rohár
2020-07-10 20:08                   ` Bjorn Helgaas
2020-07-13  8:27             ` Pali Rohár
2020-07-13 11:23               ` Lorenzo Pieralisi
2020-07-13 14:50                 ` Pali Rohár
2020-07-13 16:41                   ` Lorenzo Pieralisi
2020-07-14  7:38                     ` Pali Rohár
2020-07-15 12:17                 ` Pali Rohár
2020-07-15 16:21                   ` Lorenzo Pieralisi
2020-07-21  8:57                     ` Pali Rohár
2020-07-21 10:48                       ` Lorenzo Pieralisi

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